Civil Engineering Reference
In-Depth Information
TABLE 4.11
Relation between the Ratio of Pile Deflection to the Diameter
and the Skin Friction Capacity
Soil Type
z/D
Pile Axial Deflection for Different Pile
Diameters, mm
t/t
max
24″
36″
48″
Clays
0.0016
0.98
1.46
2.0
0.30
0.0031
1.89
2.83
3.8
0.50
0.0057
3.5
5.21
7.0
0.75
0.0080
4.9
7.32
9.8
0.90
0.0100
6.1
9.14
12.2
1.00
0.0200
12.2
18.3
24.4
0.70
-
0.90
∞
0.70
-
0.90
Sands
z
(mm)
t/t
max
0.000
0
0
0
0.00
2.5
2.5
2.5
2.5
1.00
∞
1.00
z
= local pile deflection (in mm),
D
= pile diameter (in mm),
t
= mobilized soil-pile unit skin friction
(in lb/ft
2
or kPa) and
t
max
= maximum soil-pile unit skin friction capacity computed (in lb/ft
2
or kPa).
The ratio between the residual unit skin friction to the maximum skin fric-
tion between pile and soil t
r
/t
max
at the axial pile displacement at which it occurs
(z
r
) is affected by the soil stress-strain behavior, stress history, pipe installation
method, pile load sequence and other factors.
The value of t
r
/t
max
can range from 70% to 90%. Laboratory, in-situ or
model pile tests can provide valuable information for determining values of
t
r
/t
max
and z
r
for various soils.
The end-bearing or tip-load capacity should be determined. However, rela-
tively large pile-tip movements are required to mobilize the full end-bearing
resistance. A pile-tip displacement up to 10% of the pile diameter may be
required for full mobilization in both sand and clay soils. In the absence of
more definitive criteria, the curve in
Figure 4.6
is recommended for both
sands and clays.
Table 4.12
presents the relation between the axial displacement of the pile
relative to the pile diameter and the end-bearing capacity as a percentage of the
total end-bearing capacity.
The recommended curve is shown in
Figure 4.6
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